1. Field of the Invention
The present invention relates to an electric heater, and more particularly, to an electric heater, which electrically and mechanically protects heating means from the outside, which increases heating value and thermal conductivity by increasing contact efficiency among components, and which improves assembly efficiency and productivity.
2. Background of the Related Art
In general, an air conditioning device for a car includes a cooling system for cooling the inside of the car and a heating system for heating the inside of the car.
The cooling system includes a compressor operated by receiving power form an engine and compressing and discharging refrigerant, a condenser for condensing the refrigerant compressed and discharged from the compressor by forced wind blown from a cooling fan, an expansion valve for expanding the refrigerant passing the condenser, and an evaporator for evaporating the refrigerant passing the expansion valve. The refrigerant passing the evaporator is returned to the compressor.
Meanwhile, the heating system thermally exchanges cooling water passing a heater core out of cooling water, which passes the heater core after cooling the engine and is returned to the engine, and air blown by a fan of a blower unit, and discharges the heated air into the car.
In particular, in the heating system, the cooling water flowing around the driven engine must be sufficiently heated.
However, the engine and the cooling water are cooled to sub-zero temperature in the winter season.
Finally, the heating system has a problem in that it cannot provide an initial heating effect after the engine is driven because it takes long time to increase heat of the engine more than a predetermined temperature.
Therefore, recently, an electric heater using a PTC (Positive Temperature Coefficient) element having a constant temperature feature that resistance value is increased according to temperature rise for initial heating of the car has been invented.
The electric heater using the PTC element is arranged near a heater core mounted inside a case of an air conditioning device and directly heats the air, and so, rises the inside temperature of the car from the initial driving of the engine to the normal driving.
FIG. 1 is a sectional view of a conventional electric heater for a car as an example of the electric heater using the PTC element.
As shown in FIG. 1, the electric heater includes corrugated type radiation fins 503 having a predetermined length, upper and lower frames 501 and 502, a plurality of heating bodies 504, an internal web 505, and a wave type spring 506.
A plurality of the radiation fins 503 are arranged between the upper and lower frames 501 and 502 opposed to each other at predetermined intervals.
The heating bodies 504 are interposed between the radiation fins 503, and each of the heating bodies 504 includes metal band pieces 504a separated vertically, and a fixing member 504c made of insulating material for fixing a PTC element 504b between the metal band pieces 504a. 
The internal web 505 is arranged outside the radiation fins 503 adjacent to the upper and lower frames 501 and 502.
The wave type spring 506 is mounted between the upper frame 501 or the lower frame 502 and the internal web 505.
The radiation fins 503, the upper and lower frames 501 and 502, the heating bodies 504, the internal web 505 and the wave type spring 506 which are put on another are fixed as one assembly by a side frame 507.
Meanwhile, a terminal 508 is connected to an end portion of the metal band piece 504a to be connected to a wire, and protrudes outwardly from the side frame 507 to a predetermined length.
Unexplained reference numeral 509 designates a support band firmly fixed on the radiation fin 503.
The conventional electric heater can improve heating performance till the temperature of the engine rises since the initial driving of the engine, but has the following problems.
First, there may occur electric accidents and fires due to electric short if a great deal of conductive liquid and metal are induced from the outside because the metal band pieces 504a are not electrically insulated from the adjacent radiation fin 503.
Second, the conventional electric heater may be damaged or separated due to severe vibration of the car since the heating bodies 504 are exposed to the outside in a state where it is simply interposed between the radiation fins.
Third, the upper and lower frames 501 and 502 are fixed only by the side frame 507 in a state where they compress the wave type spring 506 and the radiation fins 503.
Thereby, the metal band piece 504a and the radiation fin 503 constituting the heating body 504 are not in well close contact with each other, and so, thermal conductivity is deteriorated.
The reason that the metal band piece 504a and the radiation fin 503 are not in well close contact with each other is that excessive pressure is applied to the side frame 507 and the external force relatively applied to the central part of the electric heater is reduced.
Fourth, the fixing band 504c mounted between the metal band pieces 504a is not charged with electricity and is hindered in heat transfer since it is made of insulating material.
Fifth, if only several heating bodies 504 of the plural heating bodies 504 mounted between the radiation fins 503 for controlling volume of electric power are charged with electricity, the PCT element 504b of the heating bodies 504 which are not charged with electricity acts as an insulator, and so, the heat transfer is partially carried out.
The reason is that the PTC element 504b is made of ceramic material which is weak in heat transfer.
Sixth, the wave type spring 506 for compressing the outside of the radiation fin 503 is mounted between the upper and lower frames 501 and 502 and the outside of the radiation fins 503.
However, the internal web 505 must be mounted to prevent buckling of the radiation fins 503 generated when excessive power is transferred to a certain position of the radiation fins 503 by the shape of the wave type spring 506, and so, the number of the components of the electric heater is increased and the assembly efficiency and productivity are deteriorated.
Seventh, an end portion of a wire connected to a power supply of the car for supplying electric power to the heating bodies 504 must be uprightly connected to the terminal 508, and so, it is very complicated to connect the wire to the terminal 508.